It is well known that temperature affects the performance of electrical circuitry. The resistance or conductivity of electrical components varies dependent on the temperature of the environment within which they are operating. Such understanding can be used to generate circuits or sensors whose output varies with temperature and as such function as temperature sensors. The output of such circuits can be a proportional to absolute temperature, PTAT, output or can be a complimentary to absolute temperature, CTAT, output. A PTAT circuit will provide an output that increases with increases in temperature whereas a CTAT circuit will provide an output that decreases with increases in temperature.
PTAT and CTAT circuits are widely used in temperature sensors, bandgap type voltage references and different analog circuits. A voltage which is proportional to absolute temperature (PTAT) may be obtained from the base-emitter voltage difference of two bipolar transistors operating at different collector current densities. A corresponding PTAT current can be generated by reflecting the base-emitter voltage difference across a resistor. With a second resistor of the same type and having the same or similar temperature coefficient (TC), the base-emitter voltage difference can be gained to the desired level.
These known circuits can suffer from mismatch arising from the currents that are used to bias the component bipolar transistors that are used to generate the PTAT voltage.